Via email, Microsoft says that the new influx came before any emails were sent to existing Hotmail users encouraging them to make the upgrade.

A company representative says, “The new accounts are a mix of Hotmail upgrades, switchers from Gmail and other services, and people opening new accounts. The spike in new accounts came after the first wave of news about Outlook.com coming out of preview hit last night.”

During the six-month preview, Outlook.com had added 60 million new members. All Hotmail users are expected to be shifted automatically to the new Outlook.com interface between now and the summer, although they will be able to keep their hotmail.com and other existing email addresses.